In previous studies we have described various aspects of adenylate cyclase, its dispersion, chromatographic behavior, kinetics with respect to metal and metal-ATP, stimulation and inhibition by adenosine, stimulation by NAD and by vanadate, the influence on its assay of nucleotide pyrophosphatase and components of ATP-regenerating systems, and the influence of membrane metal content on adrenergic receptor coupling. We have developed improved methods for assaying activity and an enzymatic procedure for preparing labeled substrate. Our immediate objectives in the proposed studies are: a) to continue our evaluation of the possible regulation of adenylate cyclase by mechanisms relying on phosphate transfer reactions and by mechanisms that may involve changes in the redox state of one or several components of the adenylate cyclase system; and b) to continue to develop larger scale chromatographic and electrophoretic techniques for purification of the adenylate cyclases from brain and liver.